Structural configurations and cooling circuits in turbine blades

ABSTRACT

A turbine blade having an airfoil defined by a concave shaped pressure side outer wall and a convex shaped suction side outer wall that connect along leading and trailing edges and, therebetween, form a radially extending chamber for receiving the flow of a coolant. The turbine blade may further include a rib configuration that partitions the chamber into radially extending flow passages. The rib configuration may include a camber line rib having a wavy profile. The wavy profile may include at least one back-and-forth “S” shape.

BACKGROUND OF THE INVENTION

This invention relates to turbine airfoils, and more particularly tohollow turbine airfoils, such as rotor or stator blades, having internalchannels for passing fluids such as air to cool the airfoils.

Combustion or gas turbine engines (hereinafter “gas turbines”) include acompressor, a combustor, and a turbine. As is well known in the art, aircompressed in the compressor is mixed with fuel and ignited in thecombustor and then expanded through the turbine to produce power. Thecomponents within the turbine, particularly the circumferentiallyarrayed rotor and stator blades, are subjected to a hostile environmentcharacterized by the extremely high temperatures and pressures of thecombustion products that are expended therethrough. In order towithstand the repetitive thermal cycling as well as the extremetemperatures and mechanical stresses of this environment, the airfoilsmust have a robust structure and be actively cooled.

As will be appreciated, turbine rotor and stator blades often containinternal passageways or circuits that form a cooling system throughwhich a coolant, typically air bled from the compressor, is circulated.Such cooling circuits are typically formed by internal ribs that providethe required structural support for the airfoil, and include multipleflow paths designed to maintain the airfoil within an acceptabletemperature profile. The air passing through these cooling circuitsoften is vented through film cooling apertures formed on the leadingedge, trailing edge, suction side, and pressure side of the airfoil.

It will be appreciated that the efficiency of gas turbines increases asfiring temperatures rise. Because of this, there is a constant demandfor technological advances that enable turbine blades to withstand everhigher temperatures. These advances sometimes include new materials thatare capable of withstanding the higher temperatures, but just as oftenthey involve improving the internal configuration of the airfoil so toenhance the blades structure and cooling capabilities. However, becausethe use of coolant decreases the efficiency of the engine, newarrangements that rely too heavily on increased levels of coolant usagemerely trade one inefficiency for another. As a result, there continuesto be demand for new airfoil designs that offer internal airfoilconfigurations and coolant circulation that improves coolant efficiency.

A consideration that further complicates design of internally cooledairfoils is the temperature differential that develops during operationbetween the airfoils internal and external structure. That is, becausethey are exposed to the hot gas path, the external walls of the airfoiltypically reside at much higher temperatures during operation than manyof the internal ribs, which, for example, may have coolant flowingthrough passageways defined to each side of them. In fact, a commonairfoil configuration includes a “four-wall” arrangement in whichlengthy inner ribs run parallel to the pressure and suction side outerwalls. It is known that high cooling efficiency can be achieved by thenear-wall flow passages that are formed in the four-wall arrangement,however, the outer walls experience a significantly greater level ofthermal expansion than the inner walls. This imbalanced growth causesstress to develop at the points at which the inner ribs and outer wallsconnect, which may cause low cyclic fatigue that can shorten the life ofthe blade. As such, the development of airfoil structures that usecoolant more efficiently while also reducing stress caused by imbalancedthermal expansion between internal and external regions remains asignificant technological industry objection.

BRIEF DESCRIPTION OF THE INVENTION

The present application thus describes a turbine blade having an airfoildefined by a concave shaped pressure side outer wall and a convex shapedsuction side outer wall that connect along leading and trailing edgesand, therebetween, form a radially extending chamber for receiving theflow of a coolant. The turbine blade may further include a ribconfiguration that partitions the chamber into radially extending flowpassages. The rib configuration may include a camber line rib having awavy profile. The wavy profile may include at least one back-and-forth“S” shape.

The present application further describes a rib configuration thatincludes a camber line rib having a wavy profile having at least twoconsecutive back-and-forth “S” shapes. The camber line rib having thewavy profile may originate near the leading edge of the airfoil and windback-and-forth across an arcing path that extends toward the trailingedge of the airfoil. The arcing path may be approximately parallel to acamber reference line of the airfoil. The rib configuration may includetraverse ribs that extend across the airfoil so to connect the camberline rib to the pressure side outer wall and/or the suction side outerwall. In certain embodiments, the traverse ribs include an angle ofconnection with the pressure side outer wall and the suction side outerwall of less than about 60 degrees.

These and other features of the present application will become apparentupon review of the following detailed description of the preferredembodiments when taken in conjunction with the drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will be more completelyunderstood and appreciated by careful study of the following moredetailed description of exemplary embodiments of the invention taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a schematic representation of an exemplary turbine engine inwhich certain embodiments of the present application may be used;

FIG. 2 is a sectional view of the compressor section of the combustionturbine engine of FIG. 1;

FIG. 3 is a sectional view of the turbine section of the combustionturbine engine of FIG. 1;

FIG. 4 is a perspective view of a turbine rotor blade of the type inwhich embodiments of the present invention may be employed;

FIG. 5 is a cross-sectional view of a turbine rotor blade having aninner wall or rib configuration according to conventional design;

FIG. 6 is a cross-sectional view of a turbine rotor blade having aninner wall configuration according to an embodiment of the presentinvention;

FIG. 7 is a cross-sectional view of a turbine rotor blade having aninner wall or rib configuration according to an alternative embodimentof the present invention;

FIG. 8 is a cross-sectional view of a turbine rotor blade having aninner wall or rib configuration according to an alternative embodimentof the present invention; and

FIG. 9 is a cross-sectional view of a turbine rotor blade having aninner wall or rib configuration according to an alternative embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As an initial matter, in order to clearly describe the current inventionit will become necessary to select certain terminology when referring toand describing relevant machine components within a gas turbine. Whendoing this, if possible, common industry terminology will be used andemployed in a manner consistent with its accepted meaning. Unlessotherwise stated, such terminology should be given a broadinterpretation consistent with the context of the present applicationand the scope of the appended claims. Those of ordinary skill in the artwill appreciate that often a particular component may be referred tousing several different or overlapping terms. What may be describedherein as being a single part may include and be referenced in anothercontext as consisting of multiple components. Alternatively, what may bedescribed herein as including multiple components may be referred toelsewhere as a single part. Accordingly, in understanding the scope ofthe present invention, attention should not only be paid to theterminology and description provided herein, but also to the structure,configuration, function, and/or usage of the component.

In addition, several descriptive terms may be used regularly herein, andit should prove helpful to define these terms at the onset of thissection. These terms and their definitions, unless stated otherwise, areas follows. As used herein, “downstream” and “upstream” are terms thatindicate a direction relative to the flow of a fluid, such as theworking fluid through the turbine engine or, for example, the flow ofair through the combustor or coolant through one of the turbine'scomponent systems. The term “downstream” corresponds to the direction offlow of the fluid, and the term “upstream” refers to the directionopposite to the flow. The terms “forward” and “aft”, without any furtherspecificity, refer to directions, with “forward” referring to the frontor compressor end of the engine, and “aft” referring to the rearward orturbine end of the engine. It is often required to describe parts thatare at differing radial positions with regard to a center axis. The term“radial” refers to movement or position perpendicular to an axis. Incases such as this, if a first component resides closer to the axis thana second component, it will be stated herein that the first component is“radially inward” or “inboard” of the second component. If, on the otherhand, the first component resides further from the axis than the secondcomponent, it may be stated herein that the first component is “radiallyoutward” or “outboard” of the second component. The term “axial” refersto movement or position parallel to an axis. Finally, the term“circumferential” refers to movement or position around an axis. It willbe appreciated that such terms may be applied in relation to the centeraxis of the turbine.

By way of background, referring now to the figures, FIGS. 1 through 4illustrate an exemplary combustion turbine engine in which embodimentsof the present application may be used. It will be understood by thoseskilled in the art that the present invention is not limited to thisparticular type of usage. The present invention may be used incombustion turbine engines, such as those used in power generation,airplanes, as well as other engine types. The examples provided are notmeant to be limiting unless otherwise stated.

FIG. 1 is a schematic representation of a combustion turbine engine 10.In general, combustion turbine engines operate by extracting energy froma pressurized flow of hot gas produced by the combustion of a fuel in astream of compressed air. As illustrated in FIG. 1, combustion turbineengine 10 may be configured with an axial compressor 11 that ismechanically coupled by a common shaft or rotor to a downstream turbinesection or turbine 13, and a combustor 12 positioned between thecompressor 11 and the turbine 13.

FIG. 2 illustrates a view of an exemplary multi-staged axial compressor11 that may be used in the combustion turbine engine of FIG. 1. Asshown, the compressor 11 may include a plurality of stages. Each stagemay include a row of compressor rotor blades 14 followed by a row ofcompressor stator blades 15. Thus, a first stage may include a row ofcompressor rotor blades 14, which rotate about a central shaft, followedby a row of compressor stator blades 15, which remain stationary duringoperation.

FIG. 3 illustrates a partial view of an exemplary turbine section orturbine 13 that may be used in the combustion turbine engine of FIG. 1.The turbine 13 may include a plurality of stages. Three exemplary stagesare illustrated, but more or less stages may be present in the turbine13. A first stage includes a plurality of turbine buckets or turbinerotor blades 16, which rotate about the shaft during operation, and aplurality of nozzles or turbine stator blades 17, which remainstationary during operation. The turbine stator blades 17 generally arecircumferentially spaced one from the other and fixed about the axis ofrotation. The turbine rotor blades 16 may be mounted on a turbine wheel(not shown) for rotation about the shaft (not shown). A second stage ofthe turbine 13 also is illustrated. The second stage similarly includesa plurality of circumferentially spaced turbine stator blades 17followed by a plurality of circumferentially spaced turbine rotor blades16, which are also mounted on a turbine wheel for rotation. A thirdstage also is illustrated, and similarly includes a plurality of turbinestator blades 17 and rotor blades 16. It will be appreciated that theturbine stator blades 17 and turbine rotor blades 16 lie in the hot gaspath of the turbine 13. The direction of flow of the hot gases throughthe hot gas path is indicated by the arrow. As one of ordinary skill inthe art will appreciate, the turbine 13 may have more, or in some casesless, stages than those that are illustrated in FIG. 3. Each additionalstage may include a row of turbine stator blades 17 followed by a row ofturbine rotor blades 16.

In one example of operation, the rotation of compressor rotor blades 14within the axial compressor 11 may compress a flow of air. In thecombustor 12, energy may be released when the compressed air is mixedwith a fuel and ignited. The resulting flow of hot gases from thecombustor 12, which may be referred to as the working fluid, is thendirected over the turbine rotor blades 16, the flow of working fluidinducing the rotation of the turbine rotor blades 16 about the shaft.Thereby, the energy of the flow of working fluid is transformed into themechanical energy of the rotating blades and, because of the connectionbetween the rotor blades and the shaft, the rotating shaft. Themechanical energy of the shaft may then be used to drive the rotation ofthe compressor rotor blades 14, such that the necessary supply ofcompressed air is produced, and also, for example, a generator toproduce electricity.

FIG. 4 is a perspective view of a turbine rotor blade 16 of the type inwhich embodiments of the present invention may be employed. The turbinerotor blade 16 includes a root 21 by which the rotor blade 16 attachesto a rotor disc. The root 21 may include a dovetail configured formounting in a corresponding dovetail slot in the perimeter of the rotordisc. The root 21 may further include a shank that extends between thedovetail and a platform 24, which is disposed at the junction of theairfoil 25 and the root 21 and defines a portion of the inboard boundaryof the flow path through the turbine 13. It will be appreciated that theairfoil 25 is the active component of the rotor blade 16 that interceptsthe flow of working fluid and induces the rotor disc to rotate. Whilethe blade of this example is a turbine rotor blade 16, it will beappreciated that the present invention also may be applied to othertypes of blades within the turbine engine 10, including turbine statorblades 17. It will be seen that the airfoil 25 of the rotor blade 16includes a concave pressure side outer wall 26 and a circumferentiallyor laterally opposite convex suction side outer wall 27 extendingaxially between opposite leading and trailing edges 28, 29 respectively.The sidewalls 26 and 27 also extend in the radial direction from theplatform 24 to an outboard tip 31. (It will be appreciated that theapplication of the present invention may not be limited to turbine rotorblades, but may also be applicable to stator blades. The usage of rotorblades in the several embodiments described herein is exemplary unlessotherwise stated.)

FIG. 5 shows an internal wall construction as may be found in a rotorblade airfoil 25 having a conventional design. As indicated, the outersurface of the airfoil 25 may be defined by a relatively thin pressureside outer wall 26 and suction side outer wall 27, which may beconnected via a plurality of radially extending and intersecting ribs60. The ribs 60 are configured to provide structural support to theairfoil 25, while also defining a plurality of radially extending andsubstantially separated flow passages 40. Typically the ribs 60 extendradially so to partition the flow passages 40 over much of the radialheight of the airfoil 25, but, as discussed more below, the flow passagemay be connected along the periphery of the airfoil so to define acooling circuit. That is, the flow passages 40 may fluidly communicateat the outboard or inboard edges of the airfoil 25, as well as via anumber of smaller crossover passages or impingement apertures (notshown) that may be positioned therebetween. In this manner certain ofthe flow passages 40 together may form a winding or serpentine coolingcircuit. Additionally, film cooling ports (not shown) may be includedthat provide outlets through which coolant is released from the flowpassages 40 onto the outer surface of the airfoil 25.

The ribs 60 may include two different types, which then, as providedherein, may be subdivided further. A first type, a camber line rib 62,is typically a lengthy rib that extends in parallel or approximatelyparallel to the camber line of the airfoil, which is a reference linestretching from the leading edge 28 to the trailing edge 29 thatconnects the midpoints between the pressure side outer wall 26 and thesuction side outer wall 27. As is often the case, the conventionalconfiguration of FIG. 5 includes two camber line ribs 62, a pressureside camber line rib 63, which also may be referred to as the pressureside inner wall given the manner in which it is offset from and close tothe pressure side outer wall 26, and a suction side camber line rib 64,which also may be referred to as the suction side inner wall given themanner in which it is offset from and close to the suction side outerwall 27. As mentioned, this type of design is often referred to ashaving a “four-wall” configuration due to the prevalent four main wallsthat include the two sidewalls 26, 27 and the two camber line ribs 63,64. It will be appreciated that the outer walls 26, 27 and the camberline ribs 62 are cast as integral components.

The second type of rib is referred to herein as a traverse rib 66.Traverse ribs 66 are the shorter ribs that are shown connecting thewalls and inner ribs of the four-wall configuration. As indicated, thefour walls may be connected by a number of the traverse ribs 66, whichmay be further classified according to which of the walls each connects.As used herein, the traverse ribs 66 that connect the pressure sideouter wall 26 to the pressure side camber line rib 63 are referred to aspressure side traverse ribs 67. The traverse ribs 66 that connect thesuction side outer wall 27 to the suction side camber line rib 64 arereferred to as suction side traverse ribs 68. Finally, the traverse ribs66 that connect the pressure side camber line rib 63 to the suction sidecamber line rib 64 are referred to as center traverse ribs 69.

In general, the purpose of four-wall internal configuration in anairfoil 25 is to provide efficient near-wall cooling, in which thecooling air flows in channels adjacent to the outer walls 26, 27 of theairfoil 25. It will be appreciated that near-wall cooling isadvantageous because the cooling air is in close proximity of the hotouter surfaces of the airfoil, and the resulting heat transfercoefficients are high due to the high flow velocity achieved byrestricting the flow through narrow channels. However, such designs areprone to experiencing low cycle fatigue due to differing levels ofthermal expansion experienced within the airfoil 25, which, ultimately,may shorten the life of the rotor blade. For example, in operation, thesuction side outer walls 27 thermally expands more than the suction sidecamber line rib 64. This differential expansion tends to increase thelength of the camber line of the airfoil 25, and, thereby, causes stressbetween each of these structures as well as those structures thatconnect them. In addition, the pressure side outer wall 26 alsothermally expands more than the cooler pressure side camber line rib 63.In this case, the differential tends to decrease the length of thecamber line of the airfoil 25, and, thereby, cause stress between eachof these structures as well as those structures that connect them. Theoppositional forces within the airfoil that, in the one case, tends todecrease the airfoil camber line and, in the other, increase it, canlead to further stress concentrations. The various ways in which theseforces manifest themselves given an airfoil's particular structuralconfiguration and the manner in which the forces are then balanced andcompensated for becomes a significant determiner of the part life of therotor blade 16.

More specifically, in a common scenario, the suction side outer wall 27tends to bow outward at the apex of its curvature as exposure to thehigh temperatures of the hot gas path cause it to thermally expand. Itwill be appreciated that the suction side camber line rib 64, being aninternal wall, does not experience the same level of thermal expansionand, therefore, does not have the same tendency to bow outward. Thecamber line rib 64 then resists the thermal growth of the outer wall 27.Because conventional designs have camber line ribs 62 formed with stiffgeometries that provide little or no compliance, this resistance and thestress concentrations that result from it can be substantial.Exacerbating the problem, the traverse ribs 66 used to connect thecamber line rib 62 to the outer wall 27 are formed with linear profilesand generally oriented at right angles in relation to the walls thatthey connect. This being the case, the traverse ribs 66 operate tobasically hold fast the “cold” spatial relationship between the outerwall 27 and the camber line rib 64 as the heated structures expand atsignificantly different rates. Accordingly, with little or no “give”built into the structure, conventional arrangements are ill-suited atdefusing the stress that concentrates in certain regions of thestructure. The differential thermal expansion bus results in low cyclefatigue issues that shorten component life.

Many different internal airfoil cooling systems and structuralconfigurations have been evaluated in the past, and attempts have beenmade to rectify this issue. One such approach proposes overcooling theouter walls 26, 27 so that the temperature differential and, thereby,the thermal growth differential are reduced. It will be appreciated,though, that the way in which this is typically accomplished is toincrease the amount of coolant circulated through the airfoil. Becausecoolant is typically air bled from the compressor, its increased usagehas a negative impact on the efficiency of the engine and, thus, is asolution that is preferably avoided. Other solutions have proposed theuse of improved fabrication methods and/or more intricate internalcooling configurations that use the same amount of coolant, but use itmore efficiently. While these solutions have proven somewhat effective,each brings additional cost to either the operation of the engine or themanufacture of the part, and does nothing to directly address the rootproblem, which is the geometrical deficiencies of conventional design inlight of how airfoils grow thermally during operation.

The present invention generally teaches certain curving or bubbled orsinusoidal or wavy internal ribs (hereinafter “wavy ribs”) thatalleviate imbalanced thermal stresses that often occur in the airfoil ofturbine blades. Within this general idea, the present applicationdescribes several ways in which this may be accomplished, which includewavy camber line ribs 62 and/or traverse ribs 66, as well as certaintypes of angled connections therebetween. It will be appreciated thatthese novel configurations—which, as delineated in the appended claims,may be employed separately or in combination—reduce the stiffness of theinternal structure of the airfoil 25 so to provide targeted flexibilityby which stress concentrations are dispersed and strain off-loaded toother structural regions that are better able to withstand it. This mayinclude, for example, off-loading to a region that spreads the strainover a larger area, or, perhaps, structure that offloads tensile stressfor a compressive load, which is typically more preferable. In thismanner, life-shortening stress concentrations and strain may be avoided.

FIGS. 6 through 8 provide cross-sectional views of a turbine rotor blade16 having an inner wall configuration according to embodiments of thepresent invention. Specifically, the present invention involves theconfiguration of ribs 60 that are typically used as both structuralsupport as well as partitions that divide hollow airfoils 25 intosubstantially separated radially extending flow passages 40 that may beinterconnects as desired to create cooling circuits. These flow passages40 and the circuits they form are used to direct a flow of coolantthrough the airfoil 25 in a particular manner so that its usage istargeted and more efficient. Though the examples provided herein areshown as they might be used in a turbine rotor blades 16, it will beappreciated that the same concepts also may be employed in turbinestator blades 17. In one embodiment, the rib configuration of thepresent invention includes a camber line rib 62 having a wavy profile.(As used herein, the term “profile” is intended to refer to the shapethe ribs have in the cross-sectional views of FIGS. 6 through 8.) Acamber line rib 62, as described above, is one of the longer ribs thattypically extend from a position near the leading edge 28 of the airfoil25 toward the trailing edge 29. These ribs are referred to as “camberline ribs” because the path they trace is approximately parallel to thecamber line of the airfoil 25, which is a reference line extendingbetween the leading edge 28 and the trailing edge 29 of the airfoil 25through a collection of points that are equidistant between the concavepressure side outer wall 26 and the convex suction side outer wall 27.According to the present application, a “wavy profile” includes one thatis noticeably curved and sinusoidal in shape, as indicated. In otherwords, the “wavy profile” is one that presents a back-and-forth “S”profile. Examples of this particular type of wavy profile are providedabove FIGS. 6 and 7.

The segment or length of the camber line rib 62 that is configured withthe wavy profile may vary depending on design criteria. In the providedexamples the wavy camber line rib 62 typically stretches from a positionnear the leading edge 28 of the airfoil 25 to a position that is beyondthe midpoint of the camber line of the airfoil 25. It will beappreciated that the wavy portion of the camber line rib 62 may beshorter in length while still providing the same types of performanceadvantages discussed herein. The number of curves as well as the lengthof the wavy segment of the camber line rib 62 may be varied to achievethe best results. In certain embodiments, the wavy camber line rib 62 ofthe present invention is defined by the number of completeback-and-forth “S” shapes it contains. In a preferred embodiment of thistype, the wavy camber line rib 62 includes at least one continuousback-and-forth “S” shape. In another embodiment, the wavy camber linerib 62 includes at least two consecutive and continuous back-and-forth“S” shapes. It will be appreciated that the examples provided in FIGS. 6and 7 each trace paths having more than two full “S” shapes. In regardto overall length, the wavy segment of the camber line rib 62 may extendfor a substantial portion of the length of the camber line of theairfoil 25. For example, as shown in FIGS. 6 and 7, in a preferredembodiment, the wavy portion of the camber line rib 62 is over 50% ofthe length of the camber line of the airfoil 25. In other words, thewavy portion of the camber line rib 62 originates near the leading edge28 of the airfoil 25 and extend rearward and well beyond the apex of thecurvature of the airfoil 25. It will be appreciated that shorter lengthsalso may be employed with performance benefits, such as wavy portions ofat least 15% of the camber line rib 62.

It will be appreciated that, given its winding profile, a wavy camberline rib 62 traces a path that varies in its directional heading. Thewavy camber line rib 62 of the present invention may still be describedas having a general arcing path across which it winds, and that thispath typically extends from an origination point near the leading edge28 and a trailing point near the trailing edge 29 of the airfoil 25. Itwill be appreciated that, in the case of a wavy camber line rib 62, itis this general arcing path that is roughly parallel to the camber lineof the airfoil 25.

Many known airfoil 25 configurations, such as the four-wall example ofFIG. 5 discussed above, include two camber line ribs 62. This type ofconfiguration may be described as having a pressure side camber line rib63 that resides nearer the pressure side outer wall 26, and a suctionside camber line rib 64 that resides nearer the suction side outer wall27. The present invention, as shown in FIGS. 6 and 7, may includeconfigurations in which both the suction side camber line rib 64 and thepressure side camber line rib 63 are formed as wavy ribs. In alternativeembodiments, only one of these camber line ribs 62 may have a wavyprofile. It will be appreciated that the present invention may also beemployed in configurations having only a single camber line rib 62.

In airfoils 25 that include two camber line ribs 62, it will beappreciated that the pressure side camber line rib 63 and the suctionside camber line rib 64 define a center flow passage 40. The wavyprofile for each of the pressure side camber line rib 63 and the suctionside camber line rib 64 may be defined relative to the shape taken bysuccessive segments of the camber line rib 62 facing center flow passage40. That is, for example, relative to the central flow passage 40, thewavy profile of the camber line rib 62 may be described as including twosuccessive segments in which a first concave segment transitions to asecond convex segment. In an alternative embodiment, the wavy profilemay include four or more successive segments in which: a first concavesegment transitions to a second convex segment; the second convexsegment transitions to a third concave segment; and the third concavesegment transitions to a fourth convex segment.

As shown in FIG. 8, an alternative embodiment includes a repetition ofconvex segments. In this type of wavy rib embodiment, it will beappreciated that the wavy profile for the camber line ribs 62 (relativeto the central flow passage) include successively stacked convexsegments. In a preferred embodiment of this type, as illustrated, thecamber line ribs 62 each includes at least four of these successivelystacked convex segments. (It will be appreciated that in this type ofembodiment, to avoid stress concentrations, a short concave segment maybe used to connect the much longer convex segments.)

The present invention teaches certain configurations of traverse ribs 66that may be employed to tune the compliancy of the airfoil 25. As usedherein, traverse ribs 66 are the shorter ribs that extend across theairfoil 25. Traverse ribs 66 are used to connect camber line ribs 62 toeither other camber line ribs or one of the outer walls 26, 27 of theairfoil 25. It will be appreciated that, configured in this way,traverse ribs 66 also serve as partitions to the flow passages 40 formedbetween the outer walls 26, 27 and the camber line ribs 62. Asillustrated, the pressure side outer wall 26 and the pressure sidecamber line rib 63 are configured to define a pressure side flow passage40 between them. Similarly, the suction side outer wall 27 and thesuction side camber line rib 64 are configured to define a suction sideflow passage 40 between them. Between the suction side camber line rib64 and the pressure side camber line rib 63, the center flow passage 40is defined. As indicated, these flow passages 40 then may be subdividedby the traverse ribs 66. In certain embodiments of the presentinvention, several pressure side traverse ribs 67 connect the pressureside outer wall 26 to the pressure side camber line rib 63. Thusly, thepressure side traverse ribs 67 divide the pressure side flow passage 40into a number of separate, axially-stacked flow passages 40. Likewise,several suction side traverse ribs 68 connect the suction side outerwall 27 to the suction side camber line rib 64 and divide the suctionside flow passage 40 into a number of separate, axially-stacked flowpassages 40. Center traverse ribs 69 connect the pressure side camberline rib 63 to the suction side camber line rib 64, and similarlypartition the center flow passage.

The camber line 62 ribs and traverse ribs 66 may be configured asradially extending walls. That is, these ribs may form the profilesshown in the cross-sectional views of FIGS. 6 through 8 while extendingradially between the two ends of the airfoil 25. In this manner, thepressure side flow passages, suction side flow passages, and center flowpassages 40 may extend radially between an inboard end that is near theinterface between the airfoil 25 and the blade root 21 and an outboardend that is near the outboard tip 31 of the airfoil 25. In usage, asupply of coolant may be delivered to one or more of the inboard ends ofthe flow passages 40 via a supply passage that extends through a bladeroot 21. It will be appreciated that the flow passages 40 may beselectively connected at their inboard or outboard ends so to create aserpentine coolant path through the airfoil 25.

The rib configuration of the present invention may include severaltraverse ribs 66 on each of the pressure and suction sides of theairfoil 25. In preferred embodiments, at least five pressure sidetraverse ribs 67 and five suction side traverse ribs 68 may be included.Multiple center traverse ribs 69 also may be provided. As shown, inpreferred embodiments, the present invention may include at least twocenter traverse ribs 69. The present invention further describes aconnection assembly by which the traverse ribs 66 connect to the outerwalls 26, 27 and/or the camber line ribs 62. It will be appreciated thatthe angle in which traverse ribs 66 intersect such walls 26, 27, 62 maybe described by an “angle of connection”. (It will be appreciated thatthe “angle of connection” referred to is the smaller of the two anglesformed on both sides of each end of a traverse rib between the traverserib and the wall it intersects.) In conventional airfoil configurations,as mentioned above, the angle of connection is a steep one, generallybeing close to 90°. It will be appreciated that steep angles like thismake for a stiff structure. The present invention teaches angles thatare less than 90° as a way in which the airfoil 25 structure, ortargeted areas of the structure, may be made more compliant. Accordingto one embodiment, as shown in FIGS. 6 and 7, at least two of thepressure side traverse ribs 67 may be configured so to have an angle ofconnection with the pressure side outer wall 26 of less than about 60degrees. According to another embodiment, as indicated, at least two ofthe suction side traverse ribs 68 may be configured so to form an angleof connection with the suction side outer wall 27 of less than about 60degrees. The center traverse ribs 69 may be similarly formed, andconfigurations of the present invention include having at least oneangle of connection of less than about 60 degrees at each of the suctionside camber line rib 64 and the pressure side camber line rib 63. Wheregreater compliance is required, embodiments may include having three ofthe pressure side traverse ribs 67 and three of the suction sidetraverse ribs 68 configured so to have an angle of connection with theouter walls 26, 27 of less than about 60 degrees, and at least two ofthe center traverse ribs 69 may be configured so to form an angle ofconnection of less than about 60 degrees at each of the suction sidecamber line rib 64 and the pressure side camber line rib 63.

The present invention further describes another manner in which traverseribs 66 may enhance structural compliancy. Traverse ribs 66 typicallyare formed having a linear profile, which, as will be appreciated,results in a stiff and unyielding configuration. Pursuant to certainembodiments of the present invention, traverse ribs 66 are configuredhaving a curved profile. Specifically, as shown in each of the examplesin FIGS. 6 through 8, the center traverse ribs 69 may include an curved,arcuate or arcing profile. With this profile, the traverse ribs 66become much more compliant and able to accommodate relative movementbetween the structural walls that they connect. The direction in whichthe curved arcing profile of the traverse rib is oriented may bemanipulated so to accommodate the types of expected stresses. Accordingto one preferred embodiment, as illustrated in FIG. 6, the arc of thecenter traverse rib 69 may be directed such that the concave face of thecenter traverse ribs 69 is directed toward the leading edge 28 of theairfoil 25. This orientation may be done to all of the center traverseribs 69 that are included in a particular structure or a fractionthereof. In an alternative embodiment, as illustrated in FIG. 7, the arcof the center traverse ribs 69 may be directed such that the convex faceof the traverse rib is directed away from the leading edge 28 of theairfoil 25. This type of profile may be used on all of center traverseribs 69 or only a fraction of them.

As shown in FIG. 9, an alternative embodiment includes a camber line rib62 that includes a repetition of concave segments. In this type of wavyrib embodiment, it will be appreciated that the wavy profile for thecamber line ribs 62 (relative to the central flow passage 40) includesuccessively stacked convex segments. In a preferred embodiment of thistype, as illustrated, the camber line ribs 62 each includes at leastfour of these successively stacked concave segments. (It will beappreciated that in this type of embodiment, to avoid stressconcentrations, a short convex segment may be used to connect the muchlonger convex segments.)

FIG. 9 also includes alternative embodiments of traverse ribs 66. Asalready mentioned, according to the present invention, center traverseribs 69 may have a curved or arcing profile. Additionally, according toalternative embodiments, pressure side and suction side traverse ribs67, 68 also may include curved profiles. Exemplary types of curvedprofiles are shown along the suction side of the airfoil 25 in FIG. 9.Specifically, as indicated, suction side and pressure side traverse rib67, 68 may form an arc between the walls they connect. The arc maybeoriented such that a convex face points towards the leading edge 28 ofthe airfoil 25. Alternatively, the arc maybe oriented such that aconcave face points towards the leading edge 28 of the airfoil 25. Asalso shown in FIG. 9, similar to camber line ribs 62, traverse ribs 66may be configured having a “S” shape. As indicated, in a preferredembodiment, this configuration may be included on center traverse ribs69. In alternative embodiments, a “S” shape may be used with eitherpressure side traverse ribs 67 or suction side traverse ribs 68 or both.Further, in a preferred embodiment, as shown toward the leading edge 28of the airfoil 25 in FIG. 9, the pressure side traverse rib 67, thesuction side traverse rib 68, and the center traverse rib 69 form a wavyprofile or “S” shape by alternating how the arcs formed by each isoriented. That is, the pressure side traverse rib 67 presents a convexface toward the leading edge 28, then the center traverse rib 69 is aconcave face toward the leading edge 28, and then the suction sidetraverse rib 68 presents a convex face toward the leading edge 28 of theairfoil 25.

According to the present invention, the internal structure of an airfoilmay include wavy ribs along the camber line direction of the airfoil. Bymaking the camber line rib 62 into a spring in this way, the internalbackbone of the airfoil may be made more compliant so that performanceadvantages may be achieved. In addition, the traverse ribs of theairfoil structure may be curved so to further soften the load path, aswell as making more compliant connections with the ribs 62 and outerwalls 26, 27 that they connect. Whereas standard linear rib designsexperience high stress and low cyclic life due to the thermal fightbetween the internal cooling cavity walls and the much hotter outerwalls, the present invention provides a spring-like construction that isbetter able to disburse stress concentrations, which, as providedherein, may be used to improve the life of the component.

As one of ordinary skill in the art will appreciate, the many varyingfeatures and configurations described above in relation to the severalexemplary embodiments may be further selectively applied to form theother possible embodiments of the present invention. For the sake ofbrevity and taking into account the abilities of one of ordinary skillin the art, all of the possible iterations is not provided or discussedin detail, though all combinations and possible embodiments embraced bythe several claims below or otherwise are intended to be part of theinstant application. In addition, from the above description of severalexemplary embodiments of the invention, those skilled in the art willperceive improvements, changes and modifications. Such improvements,changes and modifications within the skill of the art are also intendedto be covered by the appended claims. Further, it should be apparentthat the foregoing relates only to the described embodiments of thepresent application and that numerous changes and modifications may bemade herein without departing from the spirit and scope of theapplication as defined by the following claims and the equivalentsthereof.

We claim:
 1. A turbine blade comprising an airfoil defined by a concave shaped pressure side outer wall and a convex shaped suction side outer wall that connect along leading and trailing edges and, therebetween, form a radially extending chamber for receiving the flow of a coolant, the turbine blade further comprising: a rib configuration that partitions the chamber into radially extending flow passages; wherein the rib configuration includes a camber line rib having a wavy profile; wherein a camber line rib having a wavy profile comprises one that originates toward the leading edge of the airfoil and winds back-and-forth across an arcing path that extends toward the trailing edge of the airfoil, the arcing path approximately parallel to a camber reference line of the airfoil; wherein the arcing path of the camber line rib comprising a length that is at least 15% of a length of the camber reference line of the airfoil; wherein the rib configuration includes two camber line ribs in which a pressure side camber line rib comprises one residing near the pressure side outer wall, and a suction side camber line rib comprises one residing near the suction side outer wall, wherein both of the pressure side camber line rib and the suction side camber line rib comprise the wavy profile; wherein the pressure side camber line rib and the suction side camber line rib define a center flow passage therebetween; and the pressure side outer wall and the pressure side camber line rib define a pressure side flow passage therebetween; and the suction side outer wall and the suction side camber line rib define a suction side flow passage therebetween; wherein the rib configuration comprises: four pressure side traverse ribs that connect the pressure side outer wall to the pressure side camber line rib and thereby partition the pressure side flow passage; four suction side traverse ribs that connect the suction side outer wall to the suction side camber line rib and thereby partition the suction side flow passage; and two center traverse rib that connects the pressure side camber line rib to the suction side camber line rib and thereby partitions the center flow passage; wherein two of the four pressure side traverse ribs are configured so to form an angle of connection with the pressure side outer wall of less than about 60 degrees; wherein two of the four suction side traverse ribs are configured so to form an angle of connection with the suction side outer wall of less than about 60 degrees; and wherein one of the two center traverse ribs form an angle of connection of less than about 60 degrees at each of the suction side camber line rib and the pressure side camber line rib.
 2. The turbine blade according to claim 1, wherein the wavy profile comprises at least one back-and-forth “S” shape; and wherein the turbine blade comprises one of a turbine rotor blade and a turbine stator blade.
 3. The turbine blade according to claim 2, wherein a camber line rib having a wavy profile comprises one that originates near the leading edge of the airfoil and winds back-and-forth across an arcing path that extends toward the trailing edge of the airfoil, the arcing path approximately parallel to a camber reference line of the airfoil; and wherein the arcing path of the camber line rib comprising a length that is at least 50% of a length of the camber reference line of the airfoil.
 4. The turbine blade according to claim 1, wherein the wavy profile comprises at least two consecutive back-and-forth “S” shapes; wherein the turbine blade comprises a turbine rotor blade.
 5. The turbine blade according to claim 1, wherein the wavy profile for each of the pressure side camber line rib and the suction side camber line rib comprises one that, relative to the central flow passage, includes at least two successive segments in which a first concave segment transitions to a second convex segment.
 6. The turbine blade according to claim 1, wherein the wavy profile for each of the pressure side camber line rib and the suction side camber line rib comprises one that, relative to the central flow passage, includes at least four successive segments in which a first concave segment transitions to a second convex segment and the second convex segment transitions to a third concave segment and the third concave segment transitions to a fourth convex segment.
 7. The turbine blade according to claim 1, wherein the wavy profile for each of the pressure side camber line rib and the suction side camber line rib comprises one that, relative to the central flow passage, includes at least three successively stacked convex segments.
 8. The turbine blade according to claim 1, wherein the wavy profile for each of the pressure side camber line rib and the suction side camber line rib comprises one that, relative to the central flow passage, includes at least three successively stacked concave segments.
 9. The turbine blade according to claim 1, wherein the rib configuration comprises traverse ribs; and wherein each of the traverse ribs comprises one configured to extend across the airfoil so as to connect one of the camber line ribs to at least one of the pressure side outer wall, the suction side outer wall, and the other camber line rib.
 10. The turbine blade according to claim 1, wherein the rib configuration is arranged so that the pressure side flow passage, the suction side flow passage, and center flow passage extend radially between a first end positioned near an inboard boundary of the airfoil and a second end positioned near an outboard boundary of the airfoil; and wherein at least one of the pressure side flow passage, the suction side flow passage, and center flow passage connects to a supply passage which is configured to receive a flow of coolant through a root of the rotor blade during operation.
 11. The turbine blade according to claim 1, wherein three of the four pressure side traverse ribs are configured so to form an angle of connection with the pressure side outer wall of less than about 60 degrees; wherein three of the four suction side traverse ribs are configured so to form an angle of connection with the suction side outer wall of less than about 60 degrees; and wherein the two center traverse ribs form an angle of connection of less than about 60 degrees at each of the suction side camber line rib and the pressure side camber line rib.
 12. The turbine blade according to claim 1, wherein one of the center traverse ribs comprise an arc between the suction side camber line rib and the pressure side camber line rib.
 13. The turbine blade according to claim 1, wherein both of the center traverse ribs comprise an arc between the suction side camber line rib and the pressure side camber line rib; and wherein the arc of each of the two center traverse ribs comprises a concave face directed toward the leading edge.
 14. The turbine blade according to claim 1, wherein both of the center traverse ribs comprise an arc between the suction side camber line rib and the pressure side camber line rib; and wherein the arc of each of the two center traverse ribs comprises a convex face directed toward the leading edge.
 15. The turbine blade according to claim 1, wherein one of the center traverse ribs comprise a profile having a “S” shape; and wherein the “S” shape, relative to the leading edge of the airfoil, includes two successive curved faces in which a first concave face transitions to a second convex face.
 16. The turbine blade according to claim 1, wherein two of the pressure side traverse ribs comprise an arc between the pressure side camber line rib and the pressure side outer wall; and wherein two of the suction side traverse ribs comprise an arc between the suction side camber line rib and the suction side outer wall.
 17. A turbine blade comprising an airfoil defined by a concave shaped pressure side outer wall and a convex shaped suction side outer wall that connect along leading and trailing edges and, therebetween, form a radially extending chamber for receiving the flow of a coolant, the turbine blade further comprising: a rib configuration that partitions the chamber into radially extending flow passages; wherein the rib configuration includes a camber line rib having a wavy profile; wherein a camber line rib having a wavy profile comprises one that originates toward the leading edge of the airfoil and winds back-and-forth across an arcing path that extends toward the trailing edge of the airfoil, the arcing path approximately parallel to a camber reference line of the airfoil; wherein the arcing path of the camber line rib comprising a length that is at least 15% of a length of the camber reference line of the airfoil; wherein the rib configuration includes two camber line ribs in which a pressure side camber line rib comprises one residing near the pressure side outer wall, and a suction side camber line rib comprises one residing near the suction side outer wall, wherein both of the pressure side camber line rib and the suction side camber line rib comprise the wavy profile; wherein the pressure side camber line rib and the suction side camber line rib define a center flow passage therebetween; and the pressure side outer wall and the pressure side camber line rib define a pressure side flow passage therebetween; and the suction side outer wall and the suction side camber line rib define a suction side flow passage therebetween; wherein the rib configuration comprises: four pressure side traverse ribs that connect the pressure side outer wall to the pressure side camber line rib and thereby partition the pressure side flow passage; four suction side traverse ribs that connect the suction side outer wall to the suction side camber line rib and thereby partition the suction side flow passage; and two center traverse rib that connects the pressure side camber line rib to the suction side camber line rib and thereby partitions the center flow passage; wherein two of the pressure side traverse ribs comprise an arc between the pressure side camber line rib and the pressure side outer wall; and wherein two of the suction side traverse ribs comprise an arc between the suction side camber line rib and the suction side outer wall. 